Pathological sympathoexcitation: how is it achieved?

Area of Science:

• Cardiovascular Physiology
• Neuroscience
• Sleep Medicine

Background:

• Congestive heart failure (CHF) and obstructive sleep apnoea syndrome (OSAS) are linked to heightened sympathetic nervous system activity.
• Increased muscle sympathetic nerve activity (MSNA) is a common feature in both CHF and OSAS.

Purpose of the Study:

• To investigate the firing characteristics of single vasoconstrictor nerve fibres in patients with CHF and OSAS.
• To determine the mechanisms underlying augmented vasoconstrictor output in these conditions at rest and during sympathoexcitatory stimuli.

Main Methods:

• Microneurographic recordings of single vasoconstrictor fibres in the muscle vascular bed.
• Analysis of firing characteristics, including firing probability and within-burst firing, at rest and during simulated sympathoexcitatory stimuli.

Main Results:

• Both CHF and OSAS patients exhibit increased firing probability at rest.
• OSAS patients show increased multiple within-burst firing at rest, unlike CHF patients.
• Both groups demonstrate a shift towards multiple within-burst firing during sympathoexcitatory stimuli.
• Evidence suggests recruitment of previously inactive vasoconstrictor fibres contributes to transient responses.

Conclusions:

• Pathological sympathoexcitation in CHF and OSAS involves both increased firing frequency and fibre recruitment.
• A shift towards increased multiple within-burst firing may be an independent risk factor due to elevated neurotransmitter release.